Project Summary The first motor behaviors produced by vertebrate animals, including humans, begin prior to birth in the form of embryonic motility and fetal breathing movements. The absence of these embryonic behaviors leads to serious decrements in muscle and lung function. Early motor behaviors can be studied in vitro in the form of rhythmic spontaneous neural activity (rSNA) carried in spinal and cranial nerve tracts. rSNA appears as regular oscillations that self-organize and propagate throughout the developing CNS. Over time, signals that generate rSNA are anatomically and chemically refined to produce the specific and specialized motor circuits required at the time of birth, such as inspiration and expiration. Even though rSNA is uniquely positioned to provide instructions that transform the output and connectivity of neural networks, how rSNA is regulated and how electrical activity assists in the functional maturation of motor circuits is still speculative. Moreover, the ability of rSNA to adapt to physiological signals, via homeostatic ionic plasticity, as well as the ramifications of plasticity for embryonic health, remain unknown. To explore this topic, we will examine the neurophysiology of rSNA as it transforms into functional breathing-related motor activity within the altricial zebra finch hindbrain. Avian embryos are an ideal model to test principles of motor system development in all vertebrates, and this project exploits the in ovo developmental strategy of birds. Oviparity provides unparalleled access to developing neural circuits throughout incubation. Previously, we showed that breathing-like motor activity could be recorded day-by-day from its onset through the establishment of ventilation at ?birth?. We now know that inspiratory and expiratory motor phases exhibit changes in temporal pattern during the embryonic period, which are correlated with changes in transmitter signaling. We found avian breathing circuits are similar to mammals in their anatomical location and neurotransmitter phenotypes, establishing the bird model as a useful experimental tool. This renewal proposal will allow us to continue our investigations into the onset, maintenance and plasticity of branchiomotor rhythms. Aim 1 will test mechanisms of CO2 and pH detection on breathing-related motor behaviors day-by-day throughout motor circuit development. Published work from our laboratory shows that pH chemosensitivity influences spontaneous breathing patterns throughout incubation, but abruptly changes polarity (from inhibition to excitation) once air-breathing is established. We hypothesize that fetal breathing-related patterns, like adult ventilation, are linked to signals through the maturation of GABA synaptic transmission and chloride transport. Aim 2 will test how early primordial rhythms maintain intrinsic activity levels and resist perturbations in neural activity. We will explore periods before air breathing begins. We will also test whether alterations in rSNA leads to errors in circuit formation and the functional maturation of the respiratory system both in vitro and in vivo. Importantly, a major goal of this research is to inspire and expose students at Idaho State University to key research questions in the field of respiratory neurobiology.